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Malfunction Indicator Lamp (MIL) Diagnosis

Malfunction Indicator Lamp (MIL) Diagnosis

Diagnostic Instructions


• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• Diagnostic Procedure Instructions provides an overview of each diagnostic category.


Circuit/System Description

The malfunction indicator lamp (MIL) illuminates to inform the driver that an emission system fault has occurred and the engine control system requires service. The ignition voltage is fed directly into MIL and when the fault in the evaporator system occurs the engine control module (ECM) sets ON MIL by grounding the MIL control circuit. Under normal operating conditions MIL should only be ON when the ignition is ON and the engine is OFF.

Diagnostic Aids

If the condition is intermittent, move the related harnesses and connectors with the ignition ON and the engine OFF, and with the engine operating while monitoring the scan tool MIL control circuit status parameters. The MIL control circuit status parameters will change from OK or Not Run to Fault if there is a condition with the circuit or a connection.

Reference Information

Schematic Reference


• Engine Controls Schematics (3.0L (LF1)) Engine Controls Schematics (2.8L (LAU))

• Instrument Cluster Schematics


Connector End View Reference

Component Connector End Views

Electrical Information Reference


• Circuit Testing

• Connector Repairs

• Testing for Intermittent Conditions and Poor Connections

• Wiring Repairs


Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification


1. Ignition ON, command the MIL ON and OFF with a scan tool. The MIL should turn ON and OFF as commanded.

2. Command the MIL ON and OFF with a scan tool while observing the following control circuit status parameters:

• The MIL Control Circuit Low Voltage Test Status

• The MIL Control Circuit Open Test Status

• The MIL Control Circuit High Voltage Test Status

Each parameter should display OK or Not Run.


Circuit/System Testing

Note

MIL-related DTCs generated must be diagnosed first.



1. Ignition OFF, disconnect the harness connector listed below at the K20 ECM.

• ECM harness connector X2 with LAU

• ECM connector X1 with LF1 or LFW

2. Ignition ON, the MIL should not illuminate.

3. If the MIL is illuminated, test the MIL control circuit listed below for a short to ground. If the circuit tests normal, replace the P16 instrument cluster.

• ECM circuit terminal 12 X2 with LAU

• ECM circuit pin 46 X1 with LF1 or LFW

4. Connect a 3 A fused jumper wire between the MIL control circuit listed below and ground. The MIL should illuminate.

• ECM circuit terminal 12 X2 with LAU

• ECM circuit pin 46 X1 with LF1 or LFW

5. If the MIL illuminates, replace the K20 ECM.

6. If the MIL does not illuminate, test the MIL control circuit for a short to voltage or an open/high resistance. If the circuit is normal, check the voltage in the instrument group for short circuit to ground or open circuit/high resistance in the ignition circuit. If the circuit tests normal, replace the P16 instrument panel cluster/bulb.


Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.


• Control Module References for ECM replacement, setup, and programming.

• Instrument Cluster Replacement